This invention relates generally to pressure relief valves and specifically to a device for securing the blowdown ring of the valve. Pressure relief valves are required to be used on a large number of pressure vessels. The function of these valves is to open when a certain pressure has been reached within the vessel. The opening of the valve exhausts the pressure within the vessel. Conventionally, such valves include an outer housing into which a nozzle communicating with the pressure vessel is inserted. A disc is biased against the nozzle's opening to seal same. A large coil spring, whose tension is adjustable, biases the disc into engagement with the nozzle through a disc holder. Adjusting tension of the coil spring alters the pressure at which the disc will unseat from the nozzle or "pop". After the pressure has been exhausted from the vessel, the combination of spring bias and blowdown ring setting will cause the disc to reseat or close at a pressure below that at which the valve opened.
The nozzle has external threading and threaded thereto is a device known as a blowdown ring. The threading on the nozzle and the blowdown ring permit the blowdown ring to be axially adjusted with respect to the nozzle as the blowdown ring is turned. The axial position of the blowdown ring determines the efficiency of the huddling chamber which creates "pop" action and the pressure at which the valve will blowdown or close. Thus, in such valves, the opening pressure is adjusted by adjusting the tension of the coil spring while the closing or reseat pressure is adjusted by adjusting the position of the blowdown ring. The blowdown ring used in usual pressure relief valves generally has a knurled or a gear-like outer surface with radially extending teeth. The purpose of the teeth is to permit the blowdown ring to be secured in place with respect to the nozzle by means of an external locking device which extends through the outer housing. However, the fact that an opening must be made in the housing for the locking device, seriously compromises the pressure integrity of the housing and the valve as a whole. The opening can provide an escape point for the pressurized fluid. Any escape of pressurized fluid can be dangerous, especially if the pressure vessel contains toxic or poisonous gas or liquid. Leakage can be extremely dangerous in certain petroleum, chemical or nuclear applications and may result in the release of hazardous materials. Where the pressure relief valve design utilizes more than one blowdown or control ring, additional openings are required in the valve housing to carry the additional locking devices. It is desirable that the number of points of potential leakage in safety relief valves be reduced as much as possible.
Another problem exists with respect to the conventional blowdown ring locking devices. Because such devices are externally accessible, the possibility exists that these devices will become damaged through inadvertant contact or be intentionally tampered with. Damage or intentional tampering can cause the locking device to be disengaged from the blowdown ring which will permit the blowdown ring to become misadjusted. The radial projection of this locking device is adjustable such that accurate positioning of the locking device is possible to place the locking portion precisely between the radially extending teeth of the blowdown ring. The blowdown ring should be secured by the locking device such that rotational movement of the ring once adjusted is prevented but no rigid contact exists between the locking device and the blowdown ring. (Misadjustment of the locking device which results in external forces on the blowdown ring may cause faulty valve performance such as leakage.) Furthermore, damage or tampering may cause the external locking device to be removed which will completely jeopardize the pressure security of the valve. Even though safety codes, which govern the construction of such valves, generally require the locking device to be sealed, such seals can easily be broken and thus provide no real security for the locking device.
Generally speaking, in accordance with the invention an improved safety relief valve and an improved locking device for its blowdown ring is provided. The locking device is not externally accessible when installed in closed discharge systems so that it in no way compromises the pressure integrity of the valve and does not permit intentional or accidental misadjustment. The device includes an annular collar surrounding the nozzle and the blowdown ring. A first releasable locking means is used to rotatably secure the blowdown ring to the annular collar. Second releasable locking means are provided to lock the collar against movement to the nozzle. The locking means can be disengaged to permit adjustment of the blowdown ring. The locking device permits the internal use of a seal required by most safety codes so that it will meet the code without the need for any amendments.
Accordingly, it is an object of this invention to provide an improved pressure relief valve and a blowdown ring locking device to secure the blowdown ring of the valve at a desired axial position along the nozzle.
It is another object of this invention to provide an improved pressure relief valve having a locking device for the blowdown ring which is not externally accessible and which prevents intentional or accidental misadjustment.
It is another object of this invention to provide an improved pressure relief valve that permits secure adjustment of the blowdown ring without introducing any external loads or forces on the blowdown ring.
It is another object of this invention to provide an improved pressure relief valve that will meet all present safety codes.
Still other objects of this invention will become apparent upon reading of the detailed specification to follow.